As a current control element for irreversibly controlling an electric connection between nodes due to device breakage, a fuse element and an anti-fuse element are known. The fuse element connecting nodes is broken by supplied electric energy and cuts the electric connection between nodes. Meanwhile, the anti-fuse element has an insulating film for cutting the electric connection between nodes, and when the insulating film is broken by the supplied electric energy, the nodes are electrically connected.
To adequately control the electric connection between nodes, it is required to control the energy supplied to the current control element to be an appropriate value. Especially, if the supplied energy amount is out of the appropriate value when the current control element is used for a storage section, a write error or an aged degradation defect may occur, and accordingly it is important to set the supplied energy to be the appropriate value.
FIG. 2 is a characteristic view showing a relation of the storage section using the current control element between voltage applied in data writing and a defect rate (a sum of an occurrence rate of the write defect and an occurrence rate of the aged degradation). Here, a time period of applying a write voltage is identical. Referring to FIG. 2, the appropriate applied voltage (the supplied energy) to the storage section using the fuse element will be described. When the applied voltage is a voltage V1 smaller than a predetermined value, that is, the supplied energy is small, so that an amount of Joule heat generated in the fuse element becomes small, the fuse element cannot be cut completely and the rate of the write error increases. Meanwhile, when the applied voltage is a voltage V2 larger than a predetermined value, that is, the supplied energy is large, an excessive cutting current flows through the fuse element and the Joule heat generated in the fuse element becomes larger than necessary. In this case, melted conductive material may enter an adjacent region such as a wiring region outside the fuse element from the fuse element and break an insulating film excessively. This conductive material in an excessively-broken portion forms a leaking-current path between wirings due to a heating process in a post-process after the cutting of the fuse element and the aged degradation, resulting in reconnection of the wirings. As a result, the fuse element is the same state as that of the defect of cutting, which becomes a cause of the aged degradation defect.
Meanwhile, in the case of a storage section using the anti-fuse element, when the supplied energy is small, the insulating film of the anti-fuse element is not broken completely to cause a connection defect, resulting in increase of the write error rate. In addition, when the supplied energy to the anti-fuse element is large, a thermal stress is excessively applied to the circumference of an oxide film, so that a conductive characteristic is changed. For example, a cavity may be formed in the circumferential metal wirings due to occurrence of electromigration, resulting in increase of a wiring resistance. In this case, a possibility of a connection defect (due to a write error and an aged degradation) increases.
To avoid the above defects, it is required to control the energy supplied to the current control element in accordance with characteristics of the current control element formed on a semiconductor substrate.
As a technique for controlling the energy supplied to the current control element, patent literature 1 and patent literature 2 are known. In the patent literature 1, by applying an electric pulse to an evaluation fuse provided on a semiconductor substrate, a total amount of the electric energy until the evaluation fuse is cut is evaluated, and the electric energy supplied to other fuse elements is determined on the basis of this amount. In this manner, minimum electric energy required to cut the fuse element can be supplied.
Additionally, in the patent literature 2, a semiconductor device includes a control circuit for controlling an electric stress supplied to an anti-fuse element. When detecting the breakdown of the anti-fuse element, the control circuit cuts the energy applied to the anti-fuse element after a certain period passed. In this manner, the energy can be prevented from being supplied to the anti-fuse more than necessary.
Citation List:
[patent literature 1]: JP 2006-310829A
[patent literature 2]: JP 2006-196079A